1 2Export CPU topology info via sysfs. Items (attributes) are similar
3to /proc/cpuinfo.
4 51) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
6 7 physical package id of cpuX. Typically corresponds to a physical
8 socket number, but the actual value is architecture and platform
9 dependent.
10 112) /sys/devices/system/cpu/cpuX/topology/core_id:
12 13 the CPU core ID of cpuX. Typically it is the hardware platform's
14 identifier (rather than the kernel's). The actual value is
15 architecture and platform dependent.
16 173) /sys/devices/system/cpu/cpuX/topology/book_id:
18 19 the book ID of cpuX. Typically it is the hardware platform's
20 identifier (rather than the kernel's). The actual value is
21 architecture and platform dependent.
22 234) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
24 25 internel kernel map of cpuX's hardware threads within the same
26 core as cpuX
27 285) /sys/devices/system/cpu/cpuX/topology/core_siblings:
29 30 internal kernel map of cpuX's hardware threads within the same
31 physical_package_id.
32 336) /sys/devices/system/cpu/cpuX/topology/book_siblings:
34 35 internal kernel map of cpuX's hardware threads within the same
36 book_id.
37 38To implement it in an architecture-neutral way, a new source file,
39drivers/base/topology.c, is to export the 4 or 6 attributes. The two book
40related sysfs files will only be created if CONFIG_SCHED_BOOK is selected.
41 42For an architecture to support this feature, it must define some of
43these macros in include/asm-XXX/topology.h:
44#define topology_physical_package_id(cpu)
45#define topology_core_id(cpu)
46#define topology_book_id(cpu)
47#define topology_thread_cpumask(cpu)
48#define topology_core_cpumask(cpu)
49#define topology_book_cpumask(cpu)
50 51The type of **_id is int.
52The type of siblings is (const) struct cpumask *.
53 54To be consistent on all architectures, include/linux/topology.h
55provides default definitions for any of the above macros that are
56not defined by include/asm-XXX/topology.h:
571) physical_package_id: -1
582) core_id: 0
593) thread_siblings: just the given CPU
604) core_siblings: just the given CPU
61 62For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
63default definitions for topology_book_id() and topology_book_cpumask().
64 65Additionally, CPU topology information is provided under
66/sys/devices/system/cpu and includes these files. The internal
67source for the output is in brackets ("[]").
68 69 kernel_max: the maximum CPU index allowed by the kernel configuration.
70 [NR_CPUS-1]
71 72 offline: CPUs that are not online because they have been
73 HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
74 of CPUs allowed by the kernel configuration (kernel_max
75 above). [~cpu_online_mask + cpus >= NR_CPUS]
76 77 online: CPUs that are online and being scheduled [cpu_online_mask]
78 79 possible: CPUs that have been allocated resources and can be
80 brought online if they are present. [cpu_possible_mask]
81 82 present: CPUs that have been identified as being present in the
83 system. [cpu_present_mask]
84 85The format for the above output is compatible with cpulist_parse()
86[see <linux/cpumask.h>]. Some examples follow.
87 88In this example, there are 64 CPUs in the system but cpus 32-63 exceed
89the kernel max which is limited to 0..31 by the NR_CPUS config option
90being 32. Note also that CPUs 2 and 4-31 are not online but could be
91brought online as they are both present and possible.
92 93 kernel_max: 31
94 offline: 2,4-31,32-63
95 online: 0-1,3
96 possible: 0-31
97 present: 0-31
98 99In this example, the NR_CPUS config option is 128, but the kernel was
100started with possible_cpus=144. There are 4 CPUs in the system and cpu2
101was manually taken offline (and is the only CPU that can be brought
102online.)
103 104 kernel_max: 127
105 offline: 2,4-127,128-143
106 online: 0-1,3
107 possible: 0-127
108 present: 0-3
109 110See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
111as well as more information on the various cpumasks.
112